1. Field of the Invention
Example embodiments of the present invention relate to pyrimidopyrimidine derivatives, organic thin film transistors using pyrimidopyrimidine derivatives and method of fabricating the same. Various example embodiments of the present invention relate to pyrimidopyrimidine oligothiophene derivatives in which an oligothiophene having p-type semiconductor characteristics may be bonded to a pyrimidopyrimidine having n-type semiconductor characteristics positioned in the center of the molecules, thereby exhibiting both p-type and n-type semiconductor characteristics, and organic thin film transistors using the derivatives as organic semiconductor materials.
2. Description of the Related Art
General organic thin film transistors (OTFTs) may comprise a substrate, a gate electrode, an insulating layer, source-drain electrodes and/or a channel layer. Organic thin film transistors may be classified into bottom-contact (BC) OTFTs wherein a channel layer may be formed on the source-drain electrodes, and top-contact (TC) OTFTs wherein metal source-drain electrodes may be formed on a channel layer by mask deposition.
Inorganic semiconductor materials, for example, silicon (Si), have been commonly used as materials for channel layers of OTFTs. However, with increasing demand for the manufacture of large-area, flexible displays at reduced costs, organic semiconductor materials may be used as materials for channel layers rather than inorganic semiconductor materials.
Some studies focusing on organic semiconductor materials for channel layers of OTFTs have been undertaken. Lower molecular weight materials and oligomers, e.g., melocyanines, phthalocyanines, perylenes, pentacenes, C60, thiophene oligomers, and the like are of some interest. Conventional devices may have charge carrier mobilities of approximately 3.2-5.0 cm2/Vs using a pentacene single crystal, or similar structure. Other conventional devices may have a charge carrier mobility of about 0.01-0.1 cm2/Vs and an on/off current ratio (Ion/Ioff ratio) using an oligothiophene derivative.
Conventional devices are largely dependent on vacuum processes for thin film formation; the fabrication of such devices may be costly.
Higher molecular weight-based OTFTs (e.g., charge carrier mobility of 0.01-0.02 cm2/Vs) employing a polythiophene-based material (F8T2) are known. Methods for fabricating an organic thin film transistor with a charge carrier mobility of 0.01-0.04 cm2/Vs by employing polythiophene P3HT, which is a representative regioregilar polymer, are known.
Regioregular polythiophene P3H5 may show a charge carrier mobility of approximately 0.01 cm2/Vs but an off-state leakage current (e.g., 10−9 A or more), leading to a lower Ion/Ioff ratio of about 400 or less.